The invention relates to a method of reinforcing or increasing the modulus of an elastomeric matrix, and an elastomeric matrix made by the method.
The main benefit of including short fibers in an elastomeric matrix is the large increase in low strain moduli demonstrated by the elastomer. This increase in modulus can be achieved using low levels of fibers. This is due to the rheological differences between an elastomer reinforced using short fibers, as compared to such properties in an elastomer matrix that is reinforced with spherical or particulate type fillers. The expected improvement in modulus can be calculated using the semi-empirical Guth-Gold equation, EQU h=h.sub.o (1+0.67fc=1.62f.sup.2 c.sup.2),
where h is the viscosity of the composite, h.sub.o is the matrix viscosity, f is the aspect ratio (1/d) and c is the volume concentration. From this equation, it can be seen that increasing aspect ratio (at constant concentration) is the main factor of short fiber reinforcement in an elastomeric matrix, regardless of the type of material used.
One of the disadvantages of using short fiber reinforcement is that the short fibers are a foreign material in an elastomer matrix, and there is not perfect adhesion between the short fibers and the matrix. Consequently, over a long period of time, as the elastomer works, the short fibers separate from the elastomer in which they are embedded, because the fibers do not flex in the matrix in the same way as the elastomer molecules. When the fibers become separated from the elastomer, their presence becomes detrimental to the properties of the elastomer.
Accordingly, it is an object of this invention to provide a method of reinforcing an elastomer that does not rely on the presence of short fibers or other reinforcing material. It is also an object of the invention to provide a modulus gradient in an elastomer around fiber type materials in order to minimize the difference in modulus between the fiber and an elastomeric matrix, in order to minimize the separation of fiber reinforcement from its elastomeric matrix.
Other objects of the invention will be apparent from the following description and claims.